Induction melting furnace with metered discharge

ABSTRACT

An induction melting furnace comprises a melt chamber for heating a melt either directly by magnetic induction, or indirectly by magnetic induction heating of the melt chamber, or a combination of the two, and a meter chamber connected to the melt chamber for providing a metered discharge of the melt from the furnace. A gas can be injected into the furnace to provide a blanket over the surface of the melt in the melt chamber and a pressurized flush of the metered discharge of the melt from the meter chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of U.S. application Ser. No.10/200,358, filed Jul. 22, 2002, which claims the benefit of U.S.Provisional Application No. 60/307,200, filed Jul. 23, 2001, and U.S.Provisional Application No. 60/352,979 filed Jan. 30, 2002, the entiretyof each of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to electric inductionmelting furnaces, and more particularly to a multi-chamber furnacewherein a molten composition, or melt, is heated and optionally meltedin a first chamber, and a metered quantity of the melt is dischargedfrom a second chamber.

BACKGROUND OF THE INVENTION

[0003] Handling and melting a material that burns in the presence ofoxygen, such as a magnesium based composition, presents special processcontrol problems. For example, at around 435° C. (nominal incipient melttemperature) and above, molten magnesium reacts violently with air bycombustion supported by oxygen in the air. At the same time, these typesof alloys are finding increased use. For example, in the automotiveindustry, lightweight magnesium alloy components, die cast or otherwiseproduced, provide a lighter vehicle with a higher fuel economy.

[0004] Early induction melting of magnesium alloys was typicallyaccomplished in an induction furnace of the type illustrated in FIG. 1.Furnace 100 comprises a crucible 102, thermal insulation 103, inductioncoils 104 a, 104 b and 104 c, magnetic shunt assembly 108, and tiltingmechanism 110. Crucible 102 was formed from a material that would notchemically react with the molten magnesium alloy 112 in the crucible. Anopen space 114 was provided between crucible 102 and thermal insulation103 to allow for the drainage of any molten material that might leakfrom the crucible. The leakage could be removed from the furnace byremoving plug 116 and draining the material. Coils 104 a, 104 b and 104c were individually controlled, and were powered from a utility sourceoperating at 50 or 60 Hertz. The general configuration of the interiorof the cylindrical crucible was a relatively large height and a smalldiameter since magnetic coupling of the field generated by currentflowing in the coils was mainly with the crucible 102, although somemagnetic flux penetrated into the molten magnesium alloy (melt) toprovide a relatively small amount of direct induction heating andmagnetic stirring of the melt. However, most heating of the melt wasaccomplished by conduction from the inductively heated crucible 102.Coils 104 a, 104 b and 104 c were selectively energized on the basis ofthe height of the melt in the crucible at any given time. Magnesiumalloy billets were used as feedstock for the furnace and lowered intothe melt by a suitable transport system. The furnace operated as a hotheel furnace in which a minimum amount (heel) of molten magnesium alloywas always left in the crucible to facilitate the conduction heating ofa billet that was added to the crucible. As mentioned above, moltenmagnesium reacts violently with oxygen in the air. Consequently, eithera cover flux or protective atmosphere was placed over the exposedsurface of the melt. Cover fluxes are low melting mixtures of salts thatmelt and flow over the surface of the melt to form a film that reducesvaporization and oxidation. However, fluxes create a corrosiveatmosphere and can cause corrosion problems in castings that are pouredfrom the molten magnesium alloy. Protective atmospheres are generallymixtures of air with sulfur dioxide, or carbon dioxide and/or sulfurhexafluoride, and are commonly used to modify the oxide film formed onthe surface of the melt to suppress vaporization and further oxidation.As an alternative to using a protective atmosphere to form a surfaceoxide coating, an inert gas, such as argon or helium (provided that theprotective volume is enclosed for this lighter than air gas), can beused to prevent magnesium from burning by excluding air from the surfaceof the melt. Tilting mechanism 110 was used to pour the melt from thecrucible for casting. The pour, and also the addition of feedstockbillets, must be very carefully performed to minimize disturbance of theprotective flux or atmosphere that is provided over the surface of themelt in the crucible. In an alternative method for tapping the melt, asiphon tube is immersed in the melt to draw a volume of molten magnesiumalloy for a casting pour. However, the siphon tube process requirespenetration of the melt's surface. Further, the weight of the tube andthe melt contained in the siphon presents a significant handling task inmovement of the tube from within the melt to a receptacle in which themelt is released.

[0005] U.S. Pat. No. 5,908,488 (the 488 patent), entitled MagnesiumMelting Furnace and Method for Melting Magnesium, illustrates anotherapproach to melting and pouring magnesium for a casting operation. Thefurnace (1) in the 488 patent, which is configured to operate as acombustion furnace, comprises a horizontally oriented multi-chamberedfurnace consisting of a melting chamber (2), a holding chamber (4) and ameter chamber (6). Magnesium feedstock is added to the melting chamberin which it melts and flows to the holding chamber. In the holdingchamber, impurities filter out of the melt and the magnesium melt flowsto the meter chamber. A protective atmosphere of an air/sulfurhexafluoride mixture is used over the surfaces of the melt in thechambers. A mechanical metering pump (27) lifts molten metal out of themeter chamber and into a transfer pipe (28) that transfers the melt to adie casting machine or a transport container. The mechanical meteringpump represents an improvement over pouring or siphoning the moltenmagnesium from the furnace but introduces a mechanical component that issubjected to a harsh operating environment and is largely recognized aspractically ineffective, expensive, unreliable and, consequently, inneed of frequent maintenance.

[0006] It is an object of the present invention to provide an inductionfurnace that will safely melt and heat molten metals, including moltenmetals that react violently with air, and provide a metered draw of themelt from the furnace in a clean and efficient manner.

BRIEF SUMMARY OF THE INVENTION

[0007] In one aspect, the present invention is an apparatus for, andmethod of, heating a melt in a furnace and providing a metered dischargeof the melt from the furnace. The furnace comprises a melt chamber and ameter chamber that are interconnected by a passage.

[0008] In one example of the invention, a melt chamber stopper means caneither allow or inhibit flow of the melt between the melt and meterchambers through the connecting passage. In another example of theinvention, a valve is used to either allow or inhibit flow of the meltbetween the melt and meter chambers through the connecting passage. Inone example of the invention, a meter chamber stopper means can eitherallow or inhibit flow of a metered discharge of the melt from thefurnace. In another example of the invention, a valve is used to eitherallow or inhibit flow of a metered discharge of the melt from thefurnace.

[0009] In one example of the present invention, a meter chamber stopperrod that is connected to the meter chamber stopper means is disposedwithin a melt chamber stopper rod that is connected to the melt chamberstopper means, and the space between the meter chamber stopper rod andmelt chamber stopper rod provides a flow path for a gas that is injectedinto the melt in the furnace. When the furnace is in the heating state,flow of melt between the melt and meter chambers is allowed, and flow ofa metered discharge of the melt from the furnace is inhibited. In thisstate, the injected gas bubbles through the melt in the melt chamber tothe space above the surface of the melt in the melt chamber where itcollects to form a protective gas blanket over the melt from oxygen inthe air. When, the furnace is in the metered discharge state, flow ofmelt between the melt and meter chambers is inhibited, and flow of ametered discharge of the melt from the furnace is allowed. In thisstate, the injected gas flows into the meter chamber to flush themetered volume of melt from the chamber.

[0010] In the example of the present invention wherein valves are usedto control the flow of the melt, gas is injected into the melt chamberand meter chamber by a controlled gas supply system. Means for supplyingfeedstock to the melt chamber are also provided. Other aspects of theinvention are set forth in this specification and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For the purpose of illustrating the invention, there is shown inthe drawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

[0012]FIG. 1 is a cross sectional view of a prior art induction furnacethat is of particular use in melting magnesium alloys.

[0013]FIG. 2 is a cross sectional view of one example of the inductionmelting furnace of the present invention with the connecting passagebetween the melt and meter chambers open and the outlet passage from themeter chamber closed.

[0014]FIG. 3 is a cross sectional view of one example of the inductionmelting furnace of the present invention with the connecting passagebetween the melt and meter chambers closed and the outlet passage fromthe meter chamber open.

[0015]FIG. 4 is a cross sectional view of another example of theinduction melting furnace of the present invention illustrating anoptional meter chamber volume adjusting element.

[0016]FIG. 5 is a cross sectional view of another example of theinduction melting furnace of the present invention illustrating analternate method of injecting a gas into the furnace.

[0017]FIG. 6 is a cross sectional view of another example of theinduction melting furnace of the present invention illustrating oneexample of a feedstock feeder for the furnace.

[0018]FIG. 7 is a cross sectional view of one example of a feedstockfeeder and automated feedstock loader for one example of the inductionmelting furnace of the present invention.

[0019]FIG. 8 is a cross sectional view of another example of theinduction melting furnace of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring now to the drawings, wherein like numerals indicatelike elements there is shown in FIG. 2 and FIG. 3 one example of aninduction melting furnace 10 of the present invention. The furnacecomprises two chambers, namely melt chamber 12 and meter chamber 14.When the melt is a magnesium based alloy, such as the general castingmagnesium alloy AZ91, one suitable non-reacting material for thechambers is a stainless steel, which is also an electrically conductivematerial. Induction coil 16 is disposed around the furnace. The coil isconnected to a suitable ac power source (not shown in the drawings) sothat the magnetic field generated from ac current flowing through thecoil inductively heats the melt chamber and the meter chamber, when theyare constructed of electrically conductive material, and/or inductivelyheats the melt when it is an electrically conductive material. Inexamples wherein the material of a chamber is electrically conductive,the chamber is inductively heated, and the induced heat is conductedinto the melt to heat the melt. For a melt such as a magnesium basedalloy, an appreciable amount of the induced heating is in the chambermaterial, although there is also some induced heating of the melt. Inother examples of the invention, most, if not all, induced heating mayoccur in the melt when the melt is an electrically conductive material,and the chambers are constructed from non-electrically conductivematerials. The illustrated configuration of the furnace is anon-limiting example of a suitable two-chamber furnace for practicingthe invention. A layer of thermal insulation 18, such as an air-bubbledceramic composition, can be placed around the exterior of the furnace toretain heat within the furnace. The layer may also serve as anelectrical insulator between the furnace and the coil. In someembodiments, the induction coil may consist of multiple induction coils,some of which may be connected to an adjustable frequency power sourceto provide time and intensity variable heating zones and/orelectromechanical stirring of the melt in either or both chambers.Additionally one or more induction coils may partially surround regionsof the melt chamber and/or the meter chamber, and be powered from one ormore suitable power supplies. The coils may be air-cooled orwater-cooled, and may consist of solid or stranded conductors configuredin what is commonly known as Litz wire.

[0021] Interconnecting passage 20 is provided between the melt and meterchambers. In this non-limiting example, the passage is formed by meltchamber nozzle 22. The walls of melt chamber nozzle 22 rise above thebase of melt chamber 12 to assist in preventing settled particulate fromflowing into the meter chamber through passage 20. Filter screens orother filtering means may be provided to serve a similar function.

[0022] As shown in FIG. 2, melt chamber stopper 24 (spherically shapedin this non-limiting example) is in the raised position to allow freetransfer of the melt through passage 20, and the free transfer ofcirculation heat in the melt throughout the two chambers. In FIG. 2,meter chamber stopper 26 (also spherically shaped in this non-limitingexample) is in the lowered position to seat on meter chamber nozzle 28,which prevents discharge of melt from the meter chamber through outletpassage 30. In this non-limiting example, meter chamber nozzle 28 is ofsimilar construct as melt chamber nozzle 22. Meter chamber stopper rod26 a is disposed within melt chamber stopper rod 24 a. Volume 60 definesa space between the melt chamber stopper rod and meter chamber stopperrod that forms a path for gas from gas supply 62 via connecting element64. A non-limiting choice of gas is an inert gas, such as argon. Eitherthe gas supply and associated connecting element 64 are commonly mountedwith melt chamber stopper rod 24 a so that it travels with the motion ofthe stopper rod, or a flexible connecting element 64 is provided toallow travel of the stopper rod while the gas supply remains fixed.Sealing element 68 prevents the escape of gas to atmosphere from volume60. Gas travels down volume 60 and exits into the melt chamber from themelt chamber stopper 24 at region 66. Gas is supplied at a pressure thatis greater than the static pressure of the melt at region 66 so that thegas bubbles up through the melt in the melt chamber and collects overthe surface of the melt. Lid 32 may be provided for greater retention ofthe gas over the surface of the melt. Generally, but not necessarily,the lid is not gas tight to avoid the build up of excessive gaspressures within the melt chamber. Alternatively venting may beaccomplished with a sealed lid, appropriate vent conduit and controlvalve for venting the gas to atmosphere, or reclamation and recycling tothe gas supply. If the melt burns in oxygen, such as a magnesium basedcomposition, the layer of a non-oxygen containing gas, such as argon,will prevent ignition of the melt. Raising and lowering means 40 raisesor lowers the melt chamber stopper rod and stopper, and raising andlowering means 42 raises or lowers the meter chamber stopper rod andstopper. The raising or lowering of the melt chamber stopper rod andstopper can be accomplished independently of the raising or lowering ofthe meter chamber stopper rod and stopper. Each raising and loweringmeans is diagrammatically shown as a weight and lever arrangement. Inpractice, any suitable drive system can be used as a stopper raising andlowering means.

[0023]FIG. 2 illustrates the melting and heating state of furnace 10.FIG. 3 illustrates the metered pour state of furnace 10. In FIG. 3, meltchamber stopper 24 is in the lowered position and seated on melt chambernozzle 22 to inhibit flow of melt from melt chamber 12 into the meterchamber 14. Meter chamber stopper 26 is in the raised position to allowthe discharge of a measured melt (based on the volume of the meterchamber) in the meter chamber through outlet passage 30 into a suitablecontainer (not shown in the figure), such as a die casting apparatus,casting mold or ladle. In the metered pour state, gas releases fromregion 66 into meter chamber 14. The release of pressurized gas into themeter chamber flushes the melt in the meter chamber through outletpassage 30. Transition from the melting and heating state to the meteredpour state is accomplished by first lowering melt chamber stopper 24 toseat on melt chamber nozzle 22, and then raising meter chamber stopper26. Conversely, in transition from the metered pour state to the meltingand heating state, meter chamber stopper 26 is lowered to seat on meterchamber nozzle 28, and then melt chamber stopper 24 is raised. Meterchamber stopper 26 represents one example of a means for controlling theflow of the melt through the connecting passage between the melt chamberand the meter chamber, and melt chamber stopper 24 represents one methodof controlling the discharge of the melt through outlet passage 30.

[0024]FIG. 4 illustrates the use of an optional meter chamber volumeadjusting element 44 that is integral with furnace 10 in thisnon-limiting example of the invention. By lowering chamber volumeadjusting element 44 into meter chamber 14, the volume in meter chamber14 is reduced. Conversely, by raising chamber volume adjusting elementout of meter chamber 14, the volume in meter chamber 14 is increased. Inthis fashion, the metered discharge volume, or shot, of melt that isreleased from the meter chamber can be precisely controlled. In thisnon-limiting example, the meter chamber volume adjusting element 44comprises a threaded plug that is seated in the boundary wall betweenthe melt and meter chambers. The threaded connection forms a liquidtight seal between the two chambers. The plug may be raised or lowered,either manually or automatically, by a rotating control rod (not shownin the figure) that penetrates a furnace boundary, such as the base,wall or lid. The rod may be either permanently or temporarily installedin the furnace. Alternatively, a remotely controlled actuator can beinstalled on the volume adjusting element.

[0025]FIG. 5 illustrates one alternative means of supplying gas tofurnace 10. In this example, gas is provided by, gas supply 62 viaconnecting element 70 to melt chamber nozzle 22 (region 67) at apressure greater than the static pressure of the melt in the nozzle.When melt chamber stopper 24 is in the raised position, gas bubbles upthrough the melt in the melt chamber. When melt chamber stopper 24 is inthe lowered position gas flows into meter chamber 14. Other functions ofthe furnace are the same as those in the previous examples of theinvention.

[0026]FIG. 6 and FIG. 7 illustrate a means for providing a continuoussupply of a feedstock to the melt chamber. FIG. 6 illustrates onenon-limiting method of supplying the feedstock, in this example,billets, into melt chamber 12. Two billets, 80 and 80 a, sit on feedertrough 82 which is tilted into the melt chamber to allow the lowerbillet 80 to be heated and melted into the melt in the melt chamber. Asthe lower billet melts, the upper billet 80 a slides down trough 82 andis immersed in the melt and melts. An auxiliary induction coil 84 may beused to preheat the upper billet prior to immersion in the melt.Alternatively or in conjunction with the auxiliary coil, waste heat gasfrom the melt chamber can be channeled around the upper billet topreheat it. Trough 82 may be mounted on adjustable pivot 86 to allow foradjustment of the trough angle into the melt. For a trough angle(between the longitudinal length of the trough and the horizontalsurface of the melt in the melt chamber) smaller than that shown in FIG.6, less of the lower billet will be immersed in the melt, and therefore,the billet will melt at a lower rate. Adjustment of the trough anglewill be related to the volume of a metered shot of melt from meterchamber 14. The larger the volume of the meter chamber, the greater thetrough angle, since more feedstock must be melted in a given period oftime to support a periodic shot of melt from the melt chamber.

[0027]FIG. 7 illustrates one method of automatically supplying newbillets 80 c, 80 d and 80 e to feeder trough 82. The lengths of thesebillets on conveyor means 90 are perpendicularly oriented to the lengthsof billets 80, 80 a and 80 b on the feeder trough. A billet sensor meanscan be provided along feeder trough 82 to sense when billet 80 b hasmoved down trough 82 to the position of billet 80 a in FIG. 7, afterbillet 80 has melted into the melt in the melt chamber, and billet 80 ahas moved to the position of billet 80 in FIG. 7. When the billet sensormeans senses the aforesaid movement of billets, which leaves theposition on trough 82 formerly occupied by billet 80 b unoccupied,conveyor means 90 is activated to move new billet 80 c to transitiontrough 92, which delivers billet 80 c in the proper orientation to theposition on trough 82 formerly occupied by billet 80 b. In this manner,a continuous feed of billet feedstock can be supplied to the furnace'smelt chamber.

[0028] In other examples of the invention, feedstock may be supplied inalternative suitable forms, such as pre-melted liquid, slurry, orgranules, with suitable delivery means for introducing the feedstockinto the melt chamber.

[0029]FIG. 8 represents another example of induction melting furnace 11of the present invention. Induction furnace 11 includes air lock 13,melt chamber 15 and meter chamber 36. In this particular example,flanges 88 join the air lock to the melt chamber, and the melt chamberto the meter chamber. Suitable thermal insulation 19 may be providedaround the melt chamber to retain heat in the interior of the chamber.Insulation may also be provided around the meter chamber.

[0030] One or more induction coils, 21 a and 21 b, at least partiallysurround the exterior of the melting chamber and are connected to one ormore high frequency power supplies (not shown in the drawings). In oneexample of the invention, wherein the melt chamber is primarilyinduction heated (e.g., a stainless steel melt chamber) a power supplyfrequency of 3,000 Hertz is suitable. The thickness of the chamber wallis selected to optimize the inductive heating of the chamber from themagnetic field created by the flow of a high frequency current from apower supply through the one or more induction coils. The coils may beair-cooled or water-cooled, and may consist of solid or strandedconductors configured in what is commonly known as Litz wire. Generally,each coil is individually controlled so that current can beindependently adjusted in each coil to reflect heating requirementsalong the height of the crucible. For example, if the height of melt 93is only to the top of coil 21 a rather than to the top of coil 21 b asshown in FIG. 8, then coil 21 b may be de-energized while coil 21 aoperates somewhere in the range from half to full current. In oneexample of the invention, one of the two coils shown in FIG. 8 may beconnected in parallel with a tuning capacitor to form a tank circuitthat is passively energized by magnetic coupling with the fieldgenerated by current flowing in the other coil when it is connected to asuitable ac power supply. This combination of passive tank coil andactive coil results in an overall induction coil circuit with improvedpower factor. It will be appreciated that there are other configurationsand variations of coil arrangements, with single or multiple coils, thatcan be used with the induction furnace of the present invention. Forexample, an orifice induction heater may be additionally provided at theoutlet of the melt chamber near meter chamber melt inlet valve 50.Further the illustration of two coils in FIG. 8 is not intended to limitthe invention to a two-coil configuration. Additionally, an inductioncoil may be provided around meter chamber 36 to inductively heat themeter chamber and/or the melt in the chamber.

[0031] Air lock 13 is a feed chamber that serves as a means forintroducing new feedstock into the melt chamber 15 of the furnaceillustrated in FIG. 8 without disturbing the controlled environmentwithin the melt chamber as further described below. Feedstock for amagnesium alloy melt is a magnesium alloy in suitable solid orsemi-solid form. For this example, the feedstock is in the form ofbillets 91, although the feedstock could be supplied in otherconfigurations, such as spherical elements.

[0032] Preheater 81 is used to preheat billets 91 to a suitabletemperature before injection into air lock 13. Preheating is done toachieve efficient melting of a billet in the melting chamber. Typicallyfor a magnesium alloy billet, the billet is heated throughout toapproximately 400° C., which is somewhat less than the incipient melttemperature of the alloy. For the example show in FIG. 8, the preheateris an induction oven. In other examples, the preheater may be afossil-fuel fired oven. For the example shown in FIG. 8, the preheaterutilizes a single induction coil 83. Other configurations of inductioncoils are contemplated within the scope of the invention. In oneexample, an induction coil is provided for each billet to accuratelycontrol the heating of each billet in the preheater. A conveyor means(not show in FIG. 8) is used to move the billets through the preheater.Upon demand for additional feedstock in the melting chamber, a billet isejected from the preheater onto conveyor means 85 for transport througha sealable supply opening 23 (shown in the opened position in FIG. 8) inair lock 13. Once the opening 23 is sealed closed by, for example,lowering door 27, closed vacuum valve 52 opens to draw a vacuum insideof the sealed airlock. In the non-limiting configuration shown in FIG.8, vacuum pump 54 draws a vacuum on tank 56 prior to the opening ofvacuum valve 52 so that the vacuum draw in the air lock is quicklyaccomplished. After drawing a vacuum in the air lock, air lock gassupply valve 58 is opened to allow the flow of a gas from gas supplytank 61. A non-limiting choice of gas is argon. Once the sealed air lockhas been flooded with argon to bring it to a pressure approximatelyequal to the pressure in the melt chamber, sealable delivery opening 25is opened by, for example, sliding door 29 to the right, to allow abillet 91 (shown in dashed lines) placed in the air lock to enter meltchamber 15. The billet 91 will be heated and become a part of the meltin the melt chamber, which generally keeps melt 93 at a tap temperature(nominally 700° C. for a magnesium alloy) for a metered discharge fromthe furnace.

[0033] Furnace 11 in FIG. 8 operates as a hot heel furnace and alwaysmaintains at least a minimum amount of melt 93 inside the melt chamber.When sealable delivery opening 25 is closed (as shown in FIG. 8), meltchamber gas supply valve 65 supplies argon to the interior of themelting chamber above the surface of melt 93. After a billet 91 entersthe melting chamber, sealable delivery opening 25 is closed and argon inthe sealed air lock is recovered by the argon supply by evacuating theargon from the feed chamber with pump 63. After argon recovery, theinterior of the air lock is vented to atmosphere by opening vent valve69, and the air lock is ready for receipt of another billet via sealablesupply opening 23.

[0034] Meter chamber melt inlet valve 50 and outlet valve 79 remainclosed until there is a demand for a measured discharge (based on thevolume of the meter chamber) of melt 94. When meter chamber 36 does notcontain a measured discharge melt, it is normally filled with argon viaopened meter chamber gas supply valve 72. When a demand for a measureddischarge melt is made, meter chamber gas supply valve 72 closes; meterchamber inlet melt valve 50 opens and; alternatively, meter chamber gasexhaust valve 71 opens so that argon displaced by the melt entering themeter chamber flows into the argon volume above the surface of melt 93in the melt chamber, or pump 74 evacuates argon from the meter chamberto the argon supply immediately before meter chamber melt inlet valve 50opens. Once the meter chamber is filled, meter chamber melt inlet valve50 closes and meter chamber melt outlet valve 79 opens to discharge ameasured melt 94 into a suitable container 96, such as a die castingapparatus, casting mold or ladle. After emptying the measured dischargemelt 94 from meter chamber 36, argon is injected back into the meterchamber by opening closed meter chamber gas supply valve 72 to ready themeter chamber for receipt of another measured discharge melt.

[0035] Meter chamber 36 can be fabricated from stainless steel when themelt is a magnesium alloy. Flanges 88 are provided for the inlet andoutlet of meter chamber 36 as a convenient means for interchanging meterchambers of varying volumes in furnace 11. In this manner, the furnacecan efficiently accommodate containers 96 of varying sizes bydischarging an amount of melt that is appropriate for the volume of aparticular container.

[0036] Summarizing the overall operation of loading a billet 91 intofurnace 11, as illustrated in FIG. 8, with the following initialconditions: Element Condition Sealable supply opening 23 Opened Sealabledelivery opening 25 Closed Vacuum valve 52 Closed Vent valve 69 ClosedAir lock gas supply valve 58 Closed

[0037] the following steps occur:

[0038] billet 91 is injected into air lock 13;

[0039] sealable supply opening 23 is closed to seal the interior of theair lock;

[0040] vacuum valve 52 opens to draw a vacuum in the air lock;

[0041] air lock gas supply valve 58 opens to inject argon into the airlock to bring the interior of the air lock to approximately the samepressure as the pressure in the melt chamber;

[0042] sealable delivery opening 25 is opened to allow billet 91 toenter melt chamber 15;

[0043] sealable delivery opening 25 is closed after billet 91 has beendeposited in the melt chamber;

[0044] gas pump 63 reclaims argon from the interior of the air lock tothe argon supply (alternatively, this step may be omitted and the argoncan be vented to atmosphere in the following step); and

[0045] gas vent valve 69 opens to bring the inside of the air lock toatmospheric pressure so that sealable supply opening 23 can be reopenedfor receiving another billet.

[0046] Summarizing the overall operation of discharging a metereddischarge melt from furnace 11 with the following initial conditions:Element Condition Meter chamber melt inlet valve 50 Closed Meter chambermelt outlet valve 79 Closed Meter chamber gas supply valve 72 OpenedMeter chamber gas exhaust valve 71 Closed

[0047] the following steps occur:

[0048] meter chamber gas supply valve 72 closes to terminate supply ofargon to meter chamber 36;

[0049] alternatively, meter chamber gas exhaust valve 71 opens to allowargon displaced by the filling of the meter chamber with melt to flowinto the volume above the melt in the melt chamber, or pump 74 is usedto evacuate argon from the meter chamber to the argon supply;

[0050] meter chamber melt inlet valve 50 opens to allow melt to fill themeter chamber;

[0051] meter chamber melt inlet valve 50 closes after the meter chamberis filled;

[0052] meter chamber melt outlet valve 79 opens to release the metereddischarge melt 94 into a suitable container;

[0053] meter chamber gas exhaust valve 71 closes and meter chamber gassupply valve 72 opens to supply argon to the meter chamber as themetered discharge melt leaves the meter chamber; and

[0054] meter chamber melt outlet valve 79 closes after the release ofthe metered discharge melt and the meter chamber is ready for thereceipt of melt from the melt chamber.

[0055] While the above examples generally describes the melting anddischarge of a molten magnesium alloy, the induction furnace withmetered discharge of the present invention has applications within thescope of the invention for use with other materials by makingappropriate modifications as known by one skilled in the art. Further anartisan will appreciate that the supporting vacuum system, protectiveair supply system, selection of the configuration of furnace openingsand valves, and the like, can all be modified without deviating from thescope of the invention.

[0056] The foregoing examples do not limit the scope of the disclosedinvention. The scope of the disclosed invention is further set forth inthe appended claims.

1. An induction melting furnace for heating a melt and discharging ametered amount of the melt, the induction melting furnace comprising: afeed chamber having a sealable supply opening for placing a charge ofthe melt in the feed chamber, the feed chamber having a sealabledelivery opening; a melt chamber for heating the melt in the meltchamber, the melt chamber connected to the feed chamber by the sealabledelivery opening, the melt chamber having a melt chamber outlet fordischarge of the melt; an at least one induction coil at least partiallysurrounding the melt chamber; a meter chamber having a meter chamberinlet and a meter chamber outlet, the meter chamber inlet connected tothe melt chamber outlet by a connecting passage; a means for opening andclosing the connecting passage to control the flow of the melt throughthe connecting passage; and a means for opening and closing the meterchamber outlet, whereby opening the connecting passage while the meterchamber outlet is closed fills the meter chamber with the melt, andopening the meter chamber outlet while the meter chamber is filled withmelt and the connecting passage is closed discharges a metered amount ofthe melt from the meter chamber through the meter chamber outlet.
 2. Theinduction melting furnace of claim 1 wherein a magnetic field created bya flow of an ac current in the at least one induction coil inductivelyheats the melt chamber whereby the heat induced in the melt chamberheats the melt in the melt chamber by conduction.
 3. The inductionmelting furnace of claim 1 wherein a magnetic field created by a flow ofan ac current in the at least one induction coil inductively heats themelt in the melt chamber.
 4. The induction melting furnace of claim 1further comprising an at least one meter chamber induction coil at leastpartially surrounding the meter chamber.
 5. The induction meltingfurnace of claim 4 wherein a magnetic field created by a flow of an accurrent in the at least one meter chamber induction coil inductivelyheats the meter chamber whereby the heat induced in the meter chamberheats the melt in the meter chamber by conduction.
 6. The inductionmelting furnace of claim 4 wherein a magnetic field created by a flow ofan ac current in the at least one meter chamber induction coilinductively heats the melt in the meter chamber.
 7. The inductionmelting furnace of claim 1 wherein the meter chamber is detachablyconnected to the melt chamber.
 8. The induction melting furnace of claim1 further comprising a preheater for preheating the charge prior toplacing the charge in the feed chamber.
 9. The induction melting furnaceof claim 1 further comprising a gas system whereby a gas can beselectably supplied to or withdrawn from the feed chamber; selectablysupplied to the melt chamber; and selectably supplied to or withdrawnfrom the meter chamber.
 10. A method of heating a melt and discharging ametered amount of the melt, the method comprising the steps of: placingthe melt in a melt chamber having a melt chamber outlet; surrounding themelt chamber at least partially with a one or more induction coils;flowing an ac current through the one or more induction coils toinductively heat the melt chamber or the melt in the melt chamber;connecting an inlet of a meter chamber to the melt chamber outlet by amelt chamber outlet valve; connecting an outlet of the meter chamber toa meter chamber outlet value; closing the meter chamber outlet valve andopening the melt chamber outlet value to fill the meter chamber withmelt from the melt chamber; and closing the melt chamber outlet valveand opening the meter chamber outlet valve to discharge the meteredvolume of melt in the meter chamber.
 11. The method of claim 10 furthercomprising the step of selectively flowing the ac current through theone or more induction coils to inductively heat selected regions of themelt chamber or melt in the melt chamber.
 12. The method of claim 10further comprising the step of connecting a tuning capacitor in parallelwith one of the one or more induction coils to form a tank circuit andmagnetically coupling the induction coil in the tank circuit with atleast one of the other one or more induction coils to induce the accurrent in the tank circuit.
 13. The method of claim 10 furthercomprising the steps of surrounding the meter chamber at least partiallywith an at least one meter chamber induction coil and flowing an accurrent through the at least one meter chamber induction coil toinductively heat the meter chamber or the melt in the meter chamber. 14.The method of claim 10 further comprising the steps of: placing a chargeof the melt in a sealable feed chamber, a feed chamber outlet sealableconnected to the melt chamber; sealing the feed chamber; and deliveringthe charge to the melt chamber through the feed chamber outlet.
 15. Themethod of claim 14 further comprising the steps of: injecting a gas intothe volume above the melt in the melt chamber; injecting the gas intothe feed chamber to approximately the same pressure of the gas injectedinto the volume above the melt in the melt chamber before delivering thecharge to the melt chamber; withdrawing the gas from the feed chamberafter delivering the charge to the melt chamber; injecting the gas intothe meter chamber when the melt chamber outlet valve is closed and themeter chamber outlet valve is opened to displace the metered volume ofmelt discharging from the meter chamber; and withdrawing the gas fromthe meter chamber when the melt chamber outlet valve is opened and themeter chamber outlet valve is closed to permit filling of the meterchamber with melt from the melt chamber.
 16. The method of claim 15further comprising injecting the gas withdrawn from the meter chamberinto the volume above the melt in the melt chamber.
 17. The method ofclaim 14 further comprising the step of preheating the charge beforeplacing the charge in the sealable feed chamber.